FFLO superconducting state in CeCoIn5

Abstract We present specific heat data for the heavy fermion superconductor CeCoIn 5 close to the upper critical field H c2 for magnetic fields applied along the [1 0 0] crystallographic axis. For fields above 10 T , the superconducting phase transition becomes first-order. In the same field range, we observe a second specific heat anomaly within the superconducting state, which we attribute to a Fulde–Ferrell–Larkin–Ovchinnikov state.